Display apparatus

ABSTRACT

The present invention is so arranged as to include (a) gradation reference potential generating means including a group of output terminals whose voltages are determined in accordance with a voltage division ratio of one ladder resistor, so as to output gradation reference potentials, for example, of 1024, which is a 16 multiple of a required 64-gradations; (b) output terminal designating means including a memory for designating, among from the output terminals, an output terminal for each of the 64-gradations required, in accordance with the display modes; and (c) selecting means for selecting an output terminal that corresponds to an input gradation signal, among from the output terminals designated by the output terminal designating section, and for applying a voltage via the thus selected output terminal to a display screen. With this arrangement, it is possible to attain very similar gradient signal-brightness characteristics for respective display modes with high accuracy, in order to prevent a gradient display from being changed due to switchover of the display modes.

This application is a Continuation of Ser. No. 10/670,237, filed Sep.26, 2003, now U.S. Pat. No. 7,262,756 the entire content of which ishereby incorporated herein by reference in this application.

FIELD OF THE INVENTION

The present invention relates to a display apparatus such as asemi-transmissive liquid crystal display apparatus and the like, whichperforms both reflective display and transmissive display, a displaymode of the reflective display and a display mode of the transmissivedisplay being different in relationship between an applied voltage andtransmissivity or relationship between the applied voltage andreflectivity.

BACKGROUND OF THE INVENTION

In general, it is preferable for display apparatuses such as liquidcrystal display apparatuses (LCDs) that the display apparatuses havesuch a gradient characteristic that output brightness is liner withrespect to an input gradation signal. Here, a characteristic representedby a relationship between an input gradation signal value and the outputbrightness is referred to as γ characteristic. The γ characteristicspecifically refers to a proportional change of brightness L of adisplay apparatus with respect to γ-th power of an input gradationsignal value E that is inputted to the display apparatus. Thus, the γcharacteristic is represented by a formula: L=KE^(γ) (γ=2.2 to 3generally; K is constant).

As described above, in the most of the display apparatuses, the outputbrightness is not linear with respect to the input gradation signal,that is, the most of the display apparatuses have the γ characteristic.Thus, in the most of the display apparatuses, it is impossible to attaincorrect gradient display without special treatment.

Therefore, it is necessary to carry out correction in the displayapparatuses in advance by using 1/γ power of the input gradation signalvalue E, which is shown in FIG. 7 as “reverse γ character of generalimage (E¹/γ)”. Hereby, it is possible to perform correct gradientdisplay as shown in FIG. 7 as “correct γ characteristic (EY)”. Thiscorrection is referred to as γ correction. By carrying out the γcorrection, it is possible to attain the linear relationship of theoutput brightness with respect to the input gradation signal, that is,L=KE (K is constant), as the “correct γ characteristic (E^(γ))”.

Incidentally, in order to attain the γ characteristic corresponding tothe γ reverse characteristic, a γ correction circuit of the displayapparatus as shown in FIG. 8 is used. The γ correction circuit realizessuitable sixty four gradations by using each selector to select one ofsixty four output terminals, which are sectioned as sixty four stages.By doing this, the correct gradient display is attained. Note that the γcorrection circuit is, as shown in FIG. 9, built in a source driver 71of an LCD 70.

In the conventional LCD, it is impossible to change a most suitablevalue of the γ correction during operation of the LCD, after the mostsuitable value is once set. In case where a display mode is not switchedover, there is no problem with this arrangement.

However, a semi-transmissive LCD is on the market recently. Thesemi-transmissive LCD takes advantages of both of the reflection method(referred to as “mode 1”) and the transmission method (referred to as“mode 2”). In the reflection method, outside light is used while abacklight is turned off. Thus, the reflection method is used in a brightplace, for low power consumption. In a dark place, used is thetransmission method in which the backlight is used as in a conventionalmethod.

In the semi-transmissive LCD, the same image looks differently when thesemi-transmissive LCD is switched over from the transmission method tothe reflection method, because gradation-brightness characteristics ofthe transmission method and the reflection method are completelydissimilar to each other, as shown in FIG. 10. This is because appliedvoltage (V)-transmissivity (T) characteristics of the transmissionmethod and the reflection method are dissimilar to each other due todifferences between the transmission method and the reflection method interms of the transmissivity and the applied voltage, as shown in FIG.11. It should be noted that FIG. 11 only discuss on the applied voltage(V)-transmissivity (T) characteristics, but the same is true for theapplied voltage (V)-reflectivity characteristics.

Moreover, there is a case where it is desirable that respective displaymodes perform different gradation displays, because, if there is onlyone gradation setting, a user may feel strange in the display.

In view of this, as shown in FIG. 12, it is so arranged that a pluralityof characteristic curves of gradation-voltage application characteristicof a source driver are provided in advance and the characteristic curvesto be used are switched over in accordance with the switchover of thedisplay modes. In FIG. 12, there are only two settings. Of course,however, there may be provided more than two settings, so that one ofthe settings can be selected for each display mode. With thisarrangement, as shown in FIG. 13, it is possible to attain completematching of the gradation-brightness characteristics between thetransmission method and the reflection method.

As a conventional display apparatus capable of changing gradation levelsaccording to which display mode is used, for example, JapanesePublication for Unexamined Patent Application “Tokukai No. 2000-193936(published on Jul. 14, 2000) discloses a display apparatus including twotypes of reference potential generating circuits 81 and 82, as shown inFIG. 14. By selecting one of the reference potential generating circuits81 and 82 in accordance with reflection/transmission judging signal,voltage (V)-transmissivity (T) characteristics of the “transmission” and“reflection” are matched (become very similar) for each gradation, whilethe applied voltage (V)-reflectivity characteristics of the“transmission” and “reflection” are also matched (become very similar)for each gradation.

Moreover, in view of a problem that γ correction coefficients cannot beswitched over according to which mode is used, because a circuitgenerating a reference voltage for a γ correction circuit has such anarrangement voltages of the circuit are determined in accordance with avoltage division ratio (a ratio of voltage division using resistors),Japanese Publication for Unexamined Patent Application “Tokukaihei No.10-333648 (published on Dec. 18, 1998) and Japanese Publication forUnexamined Patent Application “Tokukaisho No. 63-38989 (published onFeb. 19, 1988) disclose arrangements in which information regarding areference voltage of a γ correction circuit 90 is stored in a memory 91,so that reference voltages V1 to V10 are generated by retrieving theinformation and performing D/A (from digital to analog) conversion ofthe thus retrieved information. With this arrangement, it is possible toeasily attain a γ correction coefficient arbitrarily.

However, in the conventional display apparatus disclosed in JapanesePublication for Unexamined Patent Application “Tokukai No. 2000-193936(published on Jul. 14, 2000), it is impossible to reset γ correctionvalues for the respective display modes once the γ correction values areonce set. Thus, it is impossible to switch the γ correction values whenthe display modes are switched over, so that the display modes areperformed with the most suitable γ correction values. Thus, it is aproblem that the respective display mode cannot have very similargradation-brightness characteristics with high accuracy.

Moreover, in Japanese Publication for Unexamined Patent Application“Tokukaihei No. 10-333648 (published on Dec. 18, 1998) and JapanesePublication for Unexamined Patent Application “Tokukaisho No. 63-38989(published on Feb. 19, 1988), gradation correction voltages can beswitched over only discretely. Thus, it is necessary to have a largenumber of input points of the gradation correction voltages forattaining smooth switchover of the gradation characteristics. As aresult, this art also has the problem that the respective display modecannot have very similar gradation-brightness characteristics with highaccuracy.

SUMMARY OF THE INVENTION

The present invention, which is contrived to solve the aforementionedproblems associated with the related arts, has an object to provide adisplay apparatus capable of attaining very similar gradientsignal-brightness characteristics for respective display modes with highaccuracy, in order to prevent a gradient display from being changed dueto switchover of the display modes.

In order to attain the aforementioned object, a display apparatus ofsemi-transmissive type (semi-transmissive display apparatus) of thepresent invention for performing both reflective display andtransmissive display, a display mode of the reflective display and adisplay mode of the transmissive display being different in relationshipbetween an applied voltage and transmissivity or relationship betweenthe applied voltage and reflectivity, is so arranged as to include (a) agradation reference potential generating section including two series oftwo variable resistors and a ladder resistor located between the twovariable resistors, the ladder resister outputting gradation referencepotentials of a required number of gradation levels, and each of theseries dividing a power source voltage, the gradation referencepotential generating section including a memory for storing thereinresistance value setting data for each display mode, the resistancevalue setting data being for setting resistance values of the variableresistors.

With this arrangement, the gradation reference potential generatingsection is provided with two series of two variable resistors and aladder resistor located between the two variable resistors, the ladderresister outputting gradation reference potentials of a required numberof gradation levels, each of the series dividing a power source voltage.Further, the gradation reference potential generating section includinga memory for storing therein resistance value setting data for eachdisplay mode, the resistance value setting data being for settingresistance values of the variable resistors. Thus, the resistance valuesof the variable resistors are set in accordance with the resistancevalue setting data stored in the memory. Therefore, by switching overthe resistance value setting data stored, it is possible tosubstantially attain arbitrary output of the gradation referencepotentials.

Moreover, a display apparatus of semi-transmissive type of the presentinvention for performing both reflective display and transmissivedisplay, a display mode of the reflective display and a display mode ofthe transmissive display being different in relationship between anapplied voltage and transmissivity or relationship between the appliedvoltage and reflectivity, is so arranged as to include (a) a gradationreference potential generating section including a group of outputterminals whose voltages are determined in accordance with a voltagedivision ratio of one ladder resistor, so as to output gradationreference potentials of a number greater than a required number ofgradations; (b) an output terminal designating section including amemory for designating, among from the output terminals, an outputterminal for each of the gradation of the required number, in accordancewith the display modes; and (c) a selecting section for selecting anoutput terminal that corresponds to an input gradation signal, amongfrom the output terminals designated by the output terminal designatingsection, and for applying a voltage via the thus selected outputterminal to a display screen.

According to the above invention, the gradation reference potentialgenerating section is provided with the group of output terminals whosevoltages are determined in accordance with a voltage division ratio ofone ladder resistor, so as to output gradation reference potentials of anumber greater than a required number of gradations.

Thus, only one ladder resistor is provided in this arrangement.Therefore, the size of the gradation reference potential generatingsection is not greater than in a case where a plurality of ladderresistors are provided.

Moreover, the number of the output terminals in the group is greaterthan the required number of the gradations, in order to be able tosupply the gradation reference potentials of the number greater than therequired number of gradations (gradation levels). Therefore, outputtedare the gradation reference potentials of more finely divided gradationslevels than the gradations (gradation levels) required. By selecting thegradation reference potentials among from the gradation referencepotentials of such a large number, it is possible to attain accurate γcorrection.

Moreover, the output terminal designating section, which includes amemory, designates the output terminals that are suitable for thedisplay modes, respectively for each of the gradation levels(gradations) of the required number. Further, the selector selects,among from the output terminals thus designated by the output terminaldesignating section, that output terminal which corresponds to the inputgradation signal, and applies a voltage via the thus selected outputterminal to the display panel.

Therefore, the display apparatus is provided with, for example, anon-volatile memory that is accessible via the command interface, so asto store in the non-volatile memory the γ correction values that arerespectively suitable for the plural display modes of the displayapparatus.

As a result, correct gradation display is attained, and it becomespossible to improve the quality of the display image regardless ofwhether the display is performed indoors or outdoors.

Therefore, it is possible to provide a display apparatus capable ofattaining very similar gradient signal-brightness characteristics forrespective display modes with high accuracy, in order to prevent agradient display from being changed due to switchover of the displaymodes.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a block diagram illustrating an essential part of agradient reference potential generating circuit of one embodiment of anLCD of the present invention.

FIG. 1( b) is an explanatory view illustrating data stored in anon-volatile memory of the LCD.

FIG. 2 is a block diagram schematically illustrating an overallstructure of the LCD.

FIG. 3( a) is a block diagram illustrating a gradient referencepotential generating circuit for point-by-point display.

FIG. 3( b) is a graph showing an output potential of a source line inone horizontal period.

FIG. 4( a) is a block diagram illustrating a gradient referencepotential generating circuit for line-by-line display.

FIG. 4( b) is a graph showing an output potential of a source line inone horizontal period.

FIG. 5( a) is a block diagram illustrating an essential part of agradient reference potential generating circuit of another embodiment ofthe LCD of the present invention.

FIG. 5( b) is an explanatory view illustrating data stored in anon-volatile memory of the LCD.

FIG. 6 is a graph showing relationship between an input gradation signaland an output voltage.

FIG. 7 is a graph showing relationship between the input gradationsignal and brightness.

FIG. 8 is a block diagram illustrating an arrangement of a γ correctioncircuit of a conventional LCD.

FIG. 9 is a block diagram schematically illustrating an overallarrangement of the conventional LCD

FIG. 10 is a graph showing relationship between an input gradationsignal and brightness of the transmission method and the reflectionmethod in the conventional LCD.

FIG. 11 is a graph showing relationship between an applied voltage andtransmissivity of the transmission method and the reflection method inthe conventional LCD.

FIG. 12 is a graph illustrating relationship between an input gradationsignal and an applied voltage of the transmission method and thereflection method in the conventional LCD.

FIG. 13 is a graph illustrating an input gradation signal and brightnessof the transmission method and the reflection method of an ideal LCD.

FIG. 14 is a block diagram illustrating an arrangement of a γ correctioncircuit of a another conventional LCD.

FIG. 15 is a block diagram illustrating an arrangement of a γ correctioncircuit of still another conventional LCD.

DESCRIPTION OF THE EMBODIMENTS

Described below is one embodiment of the present invention, withreference to FIG. 1( a) to FIG. 6. The present embodiment discusses anLCD as a display apparatus. However, it should be noted that the displayapparatus is not limited to such LCD, and may be any other displayapparatus in which reflective display and transmissive display aredifferent in relationship between an applied voltage and transmissivity,or relationship between the applied voltage and reflectivity.

An LCD 10 as the display apparatus of the present embodiment is, asshown in FIG. 2, provided with a display panel 1 as a display screen,and a source driver 2 and a gate driver 3. The source driver 2 and thegate driver 3 are for driving the display panel 1. The source driver 2is connected with a personal computer (PC) 5 via a command interface(I/F) 4, so that display panel 1 performs display in accordance withinstructions given from the PC 5.

The LCD 10 is of the semi-transmissive type, which is capable ofdisplaying in two modes, namely a reflection method (referred to as“mode 1”), and a transmission method (referred to as “mode 2”). When theLCD 10 performs display in the reflection method, a backlight (notshown) is turned OFF and outside light is used for the display. When theLCD 10 performs display in a dark place, the display is performed in thetransmission method by using the backlight.

In the present embodiment, the LCD 10 is provided with a non-volatilememory 6 as output terminal designating means. The non-volatile memory 6stores therein reflective display-use data 6 a and transmissivedisplay-use data 6 b.

The non-volatile memory 6 is connected to the source driver 2, so thatthe reflective display-use data 6 a and the transmissive display-usedata 6 b stored in the non-volatile memory 6 can be used by the sourcedriver 2. In other words, the non-volatile memory 6 is accessible viathe command interface 4 from the PC 5, for example. Note that thecommand interface 4 is a CPU (Central Processing Unit) bus interface ofn bits (where n is 8, 9, 16, and the like). A typical example of thecommand interface 4 is a CPU (80-type CPU) compatible with the 8080 CPU.

In the reflective display-use data 6 a and the transmissive display-usedata 6 b of the non-volatile memory 6, contained are γ correction valuesrespectively for the display modes of the LCD 10.

With this arrangement, optimum values of the reflective display-use data6 a and the transmissive display-use data 6 b are switched over inaccordance with a command, in synchronism with the switchover of thedisplay modes, such as from the mode 1 to mode 2, or vice versa. In thisway, it is possible to easily correct the reflective display-use data 6a and the transmissive display-use data 6 b to their optimum values evenwhile the LCD 10 is being operated. As a result, correct gradationdisplay is attained so that quality of display image can be improvedregardless of whether the display is performed indoors or outdoors.

Moreover, with the arrangement in which the non-volatile memory 6 isprovided, it is possible to easily set γ characteristic to its optimumvalue without having a complicate circuit, even if the γ characteristicshould be switched over in order to use a display mode other than thedisplay modes described above. Thus, the LCD 10 can have a verypractical arrangement.

Here, the following discusses a structure and a method of the LCD 10 forperforming optimum γ correction in each display mode as described above.

To begin with, as shown in FIGS. 1( a) and 1(b), a gradation referencepotential generating circuit 20 as gradation reference potentialgenerating means of the present embodiment is provided with a group ofoutput terminals 11. Voltages of the output terminals 11 are determinedin accordance with a voltage division ratio of a ladder resistor 7, soas to output gradation reference potentials respectively for gradationsof a certain multiple of the required number of gradations, 64, forexample, a 16 multiple of 64-gradations required.

Moreover, each output terminal 11 in the group is connected with theselectors 12 as selection means. The selectors 12 are connected with thenon-volatile memory 6 as output terminal designating means.

The non-volatile memory 6 designates the output terminals 11 for each of64-gradation levels that are required by the display modes. On the otherhand, the selectors 12 selects, from among the output terminals 11designated by the non-volatile memory 6, the output terminal 11 thatcorresponds to an input gradation signal, and applies a voltage via thethus selected output terminal 11 to a display panel 1.

In short, in the present embodiment, adopted as one method of the γcorrection is a method using a color palette as shown in FIGS. 1( a) and1(b).

Specifically, in order to realize, for example, 64-gradations, thegradation reference potential generating circuit 20 of the presentembodiment is so arranged as to have gradation segments that outnumberthe 64-gradations, so that sixty four of the gradation segments can beselected arbitrarily. Note that the present embodiment discuses the casewhere the required gradation number is sixty four. However, the presentinvention is not limited to this.

More specifically, as shown in FIG. 1( a), by using the selectors 12corresponding thereto, sixty four output terminals 11 are selectedarbitrarily among from 1024-output terminals respectively in onethousand and twenty four gradation segments. In this way, most suitable64-gradations are realized. In this case, as to selection of sixty fouroutput terminals 11, the output terminals that are suitable for thereflection method or the transmission method are selected, in accordancewith data stored in the non-volatile memory 6. In the presentembodiment, the gradation reference potential generating circuit 20 isprovided with 1024-output terminals 11, while 64-gradations arerequired. However, the present invention is not limited to this,provided that the gradation reference potential generating circuit 20outputs gradation reference potentials of an N multiple of the requirednumber of gradations (where N is an integer not less than 2). Asdescribed above, the present embodiment is so arranged thatN=1024/64=16. For higher accuracy in the γ correction, a larger N ispreferable.

In this method, in case of a point-by-point method in which the displayis carried out per one dot, as shown in FIGS. 3( a) and 3(b), the outputterminals 11 for the 1024-gradations (that is, the one thousand andtwenty four output terminals 11) are switched over by using asophisticated D/A (digital-to-analog) converter (DAC) 13.

However, as shown in FIGS. 4( a) and 4(b), in case of a line-by-linemethod in which the display is carried out every one horizontal period(1 H), it is necessary to have D/A converters (DAC) 13 respectively forsource lines 14. Thus, it is necessary to have the output terminals ofthe number of the source line×1024-gradations (1024 multiple of thenumber of source line). It is difficult to provide such a large numberof the output terminals 11 in the circuit. Thus, this arrangement is notso practical.

FIG. 5( a) shows a little bit more practical arrangement. In thisarrangement, a gradation reference potential generating circuit 30 asthe gradation reference potential generating means is provided with, oneside thereof, two variable resistors 15 and 16 and a ladder resistor 7located therebetween, while, on the other side, the gradation referencepotential generating circuit 30 is provided with two variable resistors17 and 18, and a ladder resistor 7 located therebetween, so as to dividea power source voltage (VOH-VOL). The ladder resistors 7 respectivelyoutput gradation reference potentials. The number of the gradationreference potentials outputted by each of the ladder resistorscorresponds to the required number of the gradation levels (gradations).

Specifically, the two sets of the ladder resistors 7 are used forgenerating positive gradation reference potentials and negativegradation reference potentials. Therefore, V0+ to V63+, which are thepositive gradation reference potentials, are drawn out from the ladderresistor 7 located on the left hand side in FIG. 5( a). Meanwhile, V63−to V0−, which are the negative gradation reference potentials, are drawnout from the ladder resistor 7 located on the right hand side in FIG. 5(a).

Moreover, the gradation reference potential generating circuit 30 isprovided with a non-volatile memory 6 storing therein data for settingresistance values respectively for display modes, so as to setresistance values R1 to R4 of the respective variable resistors 15 to18.

The gradation reference potential generating circuit 30 is provided withthe variable resistors 15 to 18. By changing the resistance values ofthe variable resistors 15 to 18, the voltages of the V0 to V63 arevaried. As to how the resistance values of the variable resistors 15 to18 are changed, in case of the reflection method the resistance valuesR1, R2, R3, and R4 are selected in the non-volatile memory 6, as shownin FIG. 5( b). On the other hand, in case of the transmission method theresistance values R1′, R2′, R3′, and R4′ are selected in thenon-volatile memory 6, as shown in FIG. 5( b).

With this arrangement, it is possible to change the gradationcharacteristic as shown in FIG. 6, thereby attaining an output voltagemost suitable for the input gradation signal.

As described above, because in reality it is not practical to have γcorrection values respectively for each gradation signal, it ispreferable to have several different γ correction values in thenon-volatile memory 6, so that the most suitable one of the γ correctionvalues is used.

As described above, in the LCD 10 of the present embodiment, thegradation reference potential generating circuit 20 is provided with agroup of the output terminals 11 whose voltages are determined inaccordance with the voltage division ratio of one ladder resistor 7, soas to output the gradation reference potentials respectively forgradations of a certain multiple of the required number of gradations,64, for example, a 16 multiple of the required number of 64-gradationrequired.

Therefore, only one ladder resistor 7 is provided in this arrangement.Thus, compared with an arrangement in which a plurality of the ladderresistors 7 are provided, the gradation reference potential generatingcircuit 20 is smaller in size.

Moreover, the group of the output terminals 11 includes the outputterminals 11 of the number corresponding to the number of the gradationreference potentials, that is, a certain multiple of the required numberof gradations, 64, for example, a 16 multiple of 64-gradations required(in short, 1024-gradations). Therefore, outputted are the gradationreference potentials of more finely divided gradations levels than thesixty four gradation levels required. By selecting the gradationreference potentials among from the gradation reference potentials ofsuch number, it is possible to attain accurate γ correction.

Moreover, the non-volatile memory 6, which is consist of a memory,designates the output terminals 11 that are suitable for the displaymodes, respectively for each of the 64-gradation levels required.Further, the selector 12 selects, among from the output terminals thusdesignated by the non-volatile memory 6, that output terminal 11 whichcorresponds to the input gradation signal, and applies a voltage via thethus selected output terminal 11 to the display panel 1.

Therefore, the LCD 10 is provided with the non-volatile memory 6 that isaccessible via the command interface 4, so as to store in thenon-volatile memory 6 the γ correction values that are respectivelysuitable for the plural display modes of the LCD 10.

As a result, it is possible to attain correct gradation display andimprove the quality of the display image irrespective of whether thedisplay is performed indoors or outdoors.

Therefore, it is possible to provided the LCD 10 in which a gradationsignal-brightness characteristics of the respective display modes arevery similar with high accuracy, in order to prevent the gradationdisplay from being changed due to the switchover of the display modes.

Moreover, the memory in the LCD 10 of the present embodiment isnon-volatile. Thus, content of the memory will not be erased by turningOFF the LCD 10.

Moreover, in the non-volatile memory 6, stored for each display mode isoutput terminal designating data that is respectively for the respective64-gradation levels required in accordance with the display mode. Byusing the output terminal designating data, it is possible to easilydesignate the output terminal for a desired gradation level for eachdisplay mode (in other words, it is possible to easily set the outputterminal for a desired gradation level for each mode).

Moreover, with the arrangement in which the non-volatile memory 6 isprovided, it is possible to easily set γ characteristic to its optimumvalue without having a complicate circuit, even if the γ characteristicshould be switched over for a display mode other than the display modesdescribed above. Thus, the LCD 10 can have a very practical arrangement.

Compared with Japanese Publication for Unexamined Patent Application“Tokukai No. 2000-193936” (published on Jul. 14, 2000) discussed above,the LCD 10 of the present embodiment is different in that only oneladder resistor 7 for deciding the gradation characteristic is provided,the non-volatile memory 6 is provided, and the values of the outputterminals 11 are controlled in accordance with the settings stored inthe non-volatile memory 6. Therefore, in the LCD 10 of the presentembodiment, switchover of the settings is also very easy because thenon-volatile memory 6 is provided therein.

Therefore, it is possible to switch the settings easily in accordancewith (a) a difference between a designed panel characteristic and anactual panel characteristic, (b) a change in panel characteristic due toa change in design, (c) and the like.

Moreover, in the LCD 10 of the present embodiment, in order to dividethe power source voltage (VOH-VOL), the gradation reference potentialgenerating circuit 30 is provided with two series, each of whichincludes two variable resistors and a ladder resistor 7 located betweenthe two variable resistors, the ladder resister 7 outputting gradationreference potentials of the required number. Further, the gradationreference potential generating circuit 30 is provided with thenon-volatile memory 6 in which the resistance value setting data isstored for each display mode, in order to set the resistance values ofthe variable resistors 15 to 18. In accordance with the resistance valuesetting data stored in the non-volatile memory 6, the resistance valuesof the variable resistors 15 to 18 are set. Therefore, by switching overthe resistance value setting data stored in the non-volatile memory 6,it is possible to substantially attain arbitrary output of the gradationreference potentials.

Therefore, it is possible to provide the LCD 10 in which a gradationsignal-brightness characteristics of the respective display modes arevery similar with each other with high accuracy, in order to thegradation display from being changed due to the switchover of thedisplay modes.

Moreover, in the LCD 10 of the present embodiment, the two sets of theladder resistors 7 are respectively used for generating the positivegradation reference potentials and the negative gradation referencepotentials. More specifically, for example, it is necessary in the LCD10 that the positive gradation reference potential and the negativereference potential are applied.

In this point, the present embodiment is so arranged that two of twosets of the variable resistors 15 to 18, that is, the four variableresistors 15 to 18 are provided. Therefore, it is possible to generatethe gradation reference potential of an arbitrary gradation level ongenerating the positive gradation reference potential and the negativegradation reference potential.

Therefore, it is possible to downsize the gradation reference potentialgenerating circuit 30, while requiring only a very small amount ofinformation to be written in the non-volatile memory 6.

Note that it is necessary to have a large number of input points of thegradation compensation voltages (in the embodiment, 10 points; however,in reality, 20 points (two times of the embodiment) is necessary for+wring/−writing) for smoothly switching over the gradationcharacteristic. On the contrary, the LCD 10 of the present embodimentrequires only two points (for both +writing/−writing, 4 points arenecessary) of data, thereby only requiring a very small amount ofinformation to be written in the non-volatile memory 6.

As described above, a display apparatus of semi-transmissive type(semi-transmissive display apparatus) of the present invention forperforming both reflective display and transmissive display, a displaymode of the reflective display and a display mode of the transmissivedisplay being different in relationship between an applied voltage andtransmissivity or relationship between the applied voltage andreflectivity, is so arranged as to include (a) gradation referencepotential generating means including two series of two variableresistors and a ladder resistor located between the two variableresistors, the ladder resistor outputting gradation reference potentialsof a required number of gradation levels, each of the series dividing apower source voltage, the gradation reference potential generating meansincluding a memory for storing therein resistance value setting data foreach display mode, the resistance value setting data being for settingresistance values of the variable resistors.

In the above arrangement, the gradation reference potential generatingmeans is provided with two series of two variable resistors and a ladderresistor located between the two variable resistors, (each seriesincluding two variable resistors and one ladder resistor), the ladderresister outputting gradation reference potentials of a required numberof gradation levels, each of the series dividing a power source voltage.Further, the gradation reference potential generating means includes amemory for storing therein resistance value setting data for eachdisplay mode, the resistance value setting data being for settingresistance values of the variable resistors. With this arrangement, theresistance values of the variable resistors are set in accordance withthe resistance value setting data stored in the memory. Therefore, byswitching over the resistance value setting data stored in the memory,it is possible to substantially attain arbitrary output of the gradationreference potentials.

Therefore, it is possible to provide a display apparatus capable ofattaining very similar gradient signal-brightness characteristics forrespective display modes with high accuracy, in order to prevent agradient display from being changed due to switchover of the displaymodes.

Moreover, the display apparatus of the present invention, having theabove arrangement, may be so arranged that the memory is non-volatile.

According this arrangement, the content in the memory will not be erasedeven if the display apparatus is turned OFF.

Furthermore, the display apparatus of the present invention, having theaforementioned arrangement, may be so arranged that the two ladderresistors respectively generate a positive gradation reference potentialand a negative gradation reference potential.

In this arrangement, the two ladder resistors are respectively used togenerate the positive gradation reference potential and the negativegradation reference potential. For example, in an LCD, it is necessaryto apply positive gradation reference potential and a negative gradationreference potential.

In this point, the present invention is so arranged that two of two setsof the variable resistors, that is, the four variable resistors areprovided in total. Therefore, it is possible to generate the gradationreference potential of an arbitrary gradation level on generating thepositive gradation reference potential and the negative gradationreference potential.

Therefore, it is possible to downsize the gradation reference potentialgenerating means, while requiring only a very small amount ofinformation to be written in the non-volatile memory.

Moreover, a display apparatus of semi-transmissive type of the presentinvention for performing both reflective display and transmissivedisplay, a display mode of the reflective display and a display mode ofthe transmissive display being different in relationship between anapplied voltage and transmissivity or relationship between the appliedvoltage and reflectivity, is so arranged as to include (a) gradationreference potential generating means including a group of outputterminals whose voltages are determined in accordance with a voltagedivision ratio of one ladder resistor so as to output gradationreference potentials of a number greater than a required number ofgradations; (b) output terminal designating means including a memory fordesignating, among from the output terminals, an output terminal foreach of the gradation of the required number, in accordance with thedisplay modes; and (c) selecting means for selecting an output terminalthat corresponds to an input gradation signal, among from the outputterminals designated by the output terminal designating means, and forapplying a voltage via the thus selected output terminal to a displayscreen.

In this arrangement, the gradation reference potential generating meansincludes a group of output terminals whose voltages are determined inaccordance with a voltage division ratio of one ladder resistor so as tooutput gradation reference potentials of a number greater than arequired number of gradations.

Thus, only one ladder resistor is provided in this arrangement.Therefore, the size of the gradation reference potential generatingmeans is not greater than in a case where a plurality of ladderresistors are provided.

Moreover, the number of the output terminals in the group is greaterthan the required number of the gradations, in order to be able tosupply the gradation reference potentials of the number greater than therequired number of gradations (gradation levels). Therefore, outputtedare the gradation reference potentials of more finely divided gradationslevels than the gradations (gradation levels) required. By selecting thegradation reference potentials among from the gradation referencepotentials of such a large number, it is possible to attain accurate γcorrection.

Furthermore, the gradation reference potential generating means may beso arranged as to include a group of output terminals for outputtinggradation reference potentials of an N multiple of a required number ofgradations, where N is an integer not less than 2.

With this arrangement, the gradation reference potentials of the Nmultiple of the required number of the gradations are provided where Nis an integer not less than 2. Therefore, outputted are the gradationreference potentials of more finely divided gradations levels than thegradations (gradation levels) required. By selecting the gradationreference potentials among from the gradation reference potentials ofsuch a large number, it is possible to attain accurate γ correction.

Moreover, the output terminal designating means, which includes amemory, designates the output terminals that are suitable for thedisplay modes, respectively for each of the gradation levels(gradations) of the required number. Further, the selector selects,among from the output terminals thus designated by the output terminaldesignating means, that output terminal which corresponds to the inputgradation signal, and applies a voltage via the thus selected outputterminal to the display panel.

Therefore, the display apparatus is provided with, for example, anon-volatile memory that is accessible via the command interface, so asto store in the non-volatile memory the γ correction values that arerespectively suitable for the plural display modes of the displayapparatus.

As a result, correct gradation display is attained, and it becomespossible to improve the quality of the display image regardless ofwhether the display is performed indoors or outdoors.

Therefore, it is possible to provide a display apparatus capable ofattaining very similar gradient signal-brightness characteristics forrespective display modes with high accuracy, in order to prevent agradient display from being changed due to switchover of the displaymodes.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe included within the scope of the following claims.

1. A display apparatus of semi-transmissive type for performing bothreflective display and transmissive display, a display mode of thereflective display and a display mode of the transmissive display beingdifferent in relationship between an applied voltage and transmissivityor relationship between the applied voltage and reflectivity, thedisplay apparatus comprising: gradation reference potential generatingmeans including a group of output terminals whose voltages aredetermined in accordance with a voltage division ratio of one ladderresistor, so as to output gradation reference potentials of a numbergreater than a required number of gradations; output terminaldesignating means including a memory for designating, among from theoutput terminals, an output terminal for each of the gradation of therequired number, in accordance with whether the display apparatus is inthe reflective display mode or the transmissive display mode; andselecting means for selecting an output terminal that corresponds to aninput gradation signal, among from the output terminals designated bythe output terminal designating means and for applying a voltage via thethus selected output terminal to a display screen, wherein the memorystores therein a first combination of the output terminals for use inthe transmissive display mode, the number of the output terminals in thefirst combination corresponding to the required number of gradations;and a second combination of the output terminals for use in thereflective display mode, the number of the output terminals in thesecond combination corresponding to the required number of gradations,the first and second combinations being different from each other. 2.The display apparatus as set forth in claim 1, wherein the memory isnon-volatile, and stores therein resistance value setting data for eachdisplay mode, the resistance value setting data being for settingresistance values of the variable resistors.
 3. The display apparatus asset forth in claim 1, wherein the gradation reference potentialgenerating means includes a group of output terminals for outputtinggradation reference potentials of an N multiple of a required number ofgradations, where N is an integer not less than 2.